MPLS Evan Roggenkamp

Introduction Multiprotocol Label Switching High-performance Found in telecommunications networks Directs data from one network node to the next based on short path labels rather then long network addresses, avoiding complex lookups in a routing table. MPLS supports a range of access technologies: T1/E1, ATM, Frame Relay, and DSL MPLS is agnostic of Layer 1 or Layer 2 protocols and can be used on any type of links. Inserts a 32-bit label in between the Layer 2 and Layer 3 headers which dubbed it as a Layer 2.5 protocol. These labels number range is 0-1,048,575. Labels 0-15 for reserved purposes therefore the useable range is 16-1,048,575. MPLS provides: traffic engineering, network convergence, failure protection, and the ability to guarantee Quality of Service (QoS) over IP. Routing information obtained using a common intra domain routing protocol such as OSPF

The Label Label: 20 bits Experimental/CoS: 3 bits TTL: 8 bits BOS (bottom-of-stack) RFC 3031 “Multiprotocol Label Switching Architecture,” lists 3 bits as “experimental.” In reality, Cisco IOS uses those bits for Code of Service

Modes MPLS can run in Frame or Cell mode. In Frame mode, it’s a packet that will have labels applied or removed. In Cell mode, it is an ATM cell.

Router Roles Label switching routers Edge Label switching routers Edge LSR’s perform lookup using routing table, and then attach a label to the packet before sending it downstream to an LSR LSR’s keep a routing table but do not perform a routing table lookup; instead, LSR’s use the contents of the label to determine the next hop.

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Components Control Plane – takes care of the routing table; also where label bindings are exchanged Data Plane – takes care of the actual forwarding of traffic In the control plane we will find many common routing protocols: – OSPF (popular with MPLS service providers} – ISIS (also popular) – EIGRP – RIP – BGP Also supports: – Label Distribution Protocol (LDP); Industry standard, not proprietary – Tag Distribution Protocol (TDP); Cisco-proprietary; depreciated – Resource Reservation Protocol (RSVP); reservation of bandwidth; traffic engineering

Misc Packets can use more than one label: this is called a label stack. MPLS VPN’s use label stacks as their form of encapsulation. Attaching a label is called a “push” or label imposition Removing a label is called a “pop” or label disposition RFC 3031: rfc3031.pdfrfc3031.pdf Basic MPLS Lab with OSPF: mplsospf_basic_lab.pdfmplsospf_basic_lab.pdf

Sources MPLS faq cisco.com RFC MPLS OSPF Lab Excellent/In-Depth MPLS Power Point Excellent video on MPLS ure=iv&src_vid=MEWIdO40U54&hd=1 Better video on MPLS ure=iv&src_vid=MEWIdO40U54&hd=1